Jeremy Hughes jedahu

Null pointer exceptions can be prevented at compile time using a simple data type borrowed from Haskell.

data Maybe a = Nothing | Just a

The Maybe type

The type class encoding in my previous post on the subject is a bit rubbish:

type class instances are classes, which have a non-zero creation cost;
they do not have self-type parameters, so are not necessarily distinguishable at the type level; and
they do not provide for derived operations.

The Maybe type I described could do with some type class instances, so let’s try out a new encoding.

I hereby claim:

To claim this, I am signing this object:

	package gettyped

	sealed abstract class Maybe[A] {
	def fold[B](nothing: => B, just: A => B): B = this match {
	case Nothing() => nothing
	case Just(a) => just(a)
	}
	}

	private final case class Nothing[A]() extends Maybe[A] {}